This invention relates to a system for transmitting information between an emitting centre and receiving stations, this system being provided with means for controlling access to the information transmitted.
The invention can be used in the transmission and display of information on television receivers for purposes of entertainment, information or education. It can advantageously be applied to system of video broadcast by means of which alphanumerical information organised into pages and magazines can be put into television lines, or to interactive video broadcast system which affords access to data bases (general information, directories, etc.) and to interactive services (transactions, messages, education) through the telephone system, or to system which permits, via a data distribution line, the telecontrol, from an emitter source, of the action of recording a preselected television programme by means of receiving equipment (such as a video tape recorder, for example).
For the distribution of information, these three systems use a method of distribution in bundles, compatible with the distribution of the television signal.
The advent of services of these types raises the question of their taxation, i.e. the implementation of a system by means of which the audiences can be identified and monitored. This question arises more generally with any broadcast service tending to make the broadcasting systems more viable by better use of the resources.
Taxation of the subscription type constitutes a both flexible and durable relationship between a service and its users. Such a method of taxation is particularly justified in broadcasting.
Taxation of the type based on consumption may also be used; this method of taxation is fundamental for "interactive" systems (where there is a dialogue between the subscriber and the information source; however, it is of secondary importance in broadcasting systems (in which information is transmitted in one direction to the subscribers). There may be intermediate systems known as "quasi-interactive" systems wherein the content of the distribution source is continuously modified to meet the requirements of the users, which are transmitted via a public data network. The advent of new distribution means with a very large capacity, such as satellites, will develop this quasi-interactive method considerably, thus making it necessary to implement a system for controlling access to the information provided.
This problem of access control raises above all the problems of locking up the information when it is broadcast and unlocking it when it is received, and naturally these problems must be resolved in accordance with the specificity of the system which is to be controlled.